Control system for cooking appliance employing convection and radiant cooking

ABSTRACT

A cooking appliance includes a heating system which is preferably capable of combining radiant, convection, microwave and conduction heating techniques to perform a cooking operation. The cooking appliance includes a convection fan and at least one heating device. A controller is provided to regulate a triac to create a variable fan speed and variable heater intensity through phase angle firing. Essentially, an AC waveform provided to the fan motor and/or the heater resistor travels through the triac which is turned on by the controller at predetermined points in the AC waveform, with the delay from a zero point waveform crossing functioning to reduce the amount of power sent to the heater resistor and fan motor. When the signal from the controller is removed, the triac advantageously turns off at the next zero crossing of the AC waveform such that an operationally and economically effective control system is provided.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/560,279 entitled “Control System for CookingAppliance Employing Convection and Radiant Cooking” filed Apr. 8, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the art of cooking appliances and,more particularly, to a system for controlling both a fan and heater ina compact cooking appliance capable of combining radiant, convection,conduction and microwave heating techniques to perform a cookingoperation.

2. Discussion of the Prior Art

There exist a wide range of cooking appliances on the market. Many ofthese cooking appliances are designed for use in cooking various typesof food products in different ways. For instance, where moreconventional cooking appliances generally relied upon radiant energy asthe sole heat source, more recent trends combine a radiant heat sourcewith convection, microwave or conduction heating techniques, therebyincreasing the versatility of the cooking appliance while potentiallyshortening required cook times. In particular, the prior art containsexamples of appliances that combine radiant and convection cooking;convection, microwave and radiant cooking; and microwave, convection andconduction heating techniques.

Regardless of the existence of these known arrangements, there stillexists a need for a cooking appliance that combines each of radiant,convection, microwave and conduction heating techniques in an efficientand effective manner to handle a wide range of food items. Particularly,there exists a need for a cooking appliance that can be used to rapidlyprepare food products that require numerous different heat sources forfull and complete cooking. For example, the rapid preparation ofcommercially produced, open-faced grilled sandwiches raises variouscooking concerns. Open-faced grilled sandwiches require, at the veryleast, that heat be directed both downward onto an upper portion of thesandwich and upward onto a lower bun portion of the sandwich. In mostcases this is accomplished by passing the open-faced sandwich on aconveyor belt through an oven between opposing radiant heat sources.While effective to a degree, the process can be time consuming andreally does not result in a uniform heating of the meat, cheese and/orother toppings on the bread, nor an even toasting of the bread itself.In addition to this potential problem, a dual radiant oven of this typeis simply not suitable for many other applications. For instance, anadditional microwave oven or the like would typically be employed toheat soup or other liquid-based food items.

Regardless of the variety of known cooking appliances, there exists theneed for a versatile cooking appliance that can preferably takeadvantage of radiant, convection, microwave and conductive cookingtechniques such that the appliance can be used to rapidly andeffectively cook a wide range of food items. When providing such aversatile cooking appliance, it is desirable to have a requisiteconvection fan run at variable speeds and the radiant heater run atdifferent output levels. In particular, during various phases of acooking operation, it is desired to alter the operation of both the fanand heater to obtain the desired cooking effect. Therefore, there existsa need for a control apparatus for a cooking appliance that caneffectively and efficiently regulate both fan speed and radiant heateroutput.

SUMMARY OF THE INVENTION

The present invention is directed to a cooking appliance including acooking chamber having top, bottom, rear and opposing side walls, atleast one radiant heating element exposed to the cooking chamber, aconvection fan, a microwave heating device having at least one rotatableantenna and a conduction heating device, all of which can be operated incombination to perform a cooking operation. The cooking appliance alsoincludes an air plenum arranged at a top portion of the cooking chamber.The air plenum is bifurcated so as to define two distinct passagesseparated by an angled divider. The angled divider defines a tapered airdelivery portion and a tapered exhaust portion within the bifurcated airplenum. The tapered air delivery portion guides a convective air flowthrough an air emitter plate positioned at the top wall of the cookingchamber.

In a preferred embodiment of the invention, the air emitter plateincludes a recessed, serpentine-like channel having a plurality ofopenings that lead to the air delivery portion. Nested within therecessed channel is the radiant heating element. With this arrangement,not only does the radiant heating element deliver radiant heat, but heatis transferred from the radiant heating element to the convectioncooking air delivered into the cooking chamber. The air currents arefurnished by a convection fan positioned in a fan housing, preferablyarranged behind the cooking chamber.

In accordance with the invention, the cooking appliance includes acooling fan arranged in a housing located behind the convection fanhousing. The cooling fan draws an ambient air flow into the cookingappliance through an air intake that extends below the cooking chamber.A first portion of the intake air flow is preferably directed to theconvection fan, while a second or major portion of the air flow is usedto cool control elements, such as control boards, electronics, relaysand the like arranged in the appliance. Preferably, the cooling fan isdrivingly connected to the convection fan. With this arrangement,activation of the cooling fan establishes both the intake air flow forcooling system components and a fresh convection air flow supply thatcombines with other heating techniques to perform the combined cookingoperation.

A particular aspect of the present invention concerns a control systemfor regulating the convection fan and radiant heater. In accordance withthe most preferred embodiment of the invention, a circuit, including arelay and a triac, is arranged on a control board. The circuit isspecifically designed to control the convection fan through phase anglefiring to run at variable speeds and the radiant heater to run atvarious output levels. By modifying the AC waveform delivered to theconvection fan and radiant heater, the control system can effectivelyalter the power delivered to these two devices in order to allow for thevariable fan speeds and variations in radiant heater output.Essentially, a microprocessor is provided to turn the triac on and offat various points in the AC waveform, thereby establishing waveformchopping operations. When the control signal from the microprocessor isremoved, the triac turns off at the next zero crossing of the waveform.By turning the AC voltage on at various points in the AC waveform, thetriac essentially limits the power going through the controlledcomponents which, in this case, constitute the fan motor and the heater.In this manner, a relatively inexpensive, yet highly effective, way ofcontrolling both the convection fan and radiant heater is achieved.

Additional objects, features and advantages of the present inventionwill become more readily apparent from the following detaileddescription of a preferred embodiment when taken in conjunction with thedrawings wherein like reference numerals refer to corresponding parts inthe several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an upper right perspective view of a cooking applianceincorporating a combination heating system constructed in accordancewith the present invention;

FIG. 2 is a front view of the cooking appliance of FIG. 1 with a cookingchamber of the appliance exposed;

FIG. 3 is an upper right perspective view of the cooking appliance ofFIG. 1 with an outer cabinet portion of the appliance removed;

FIG. 4 is a cross-sectional side view of the cooking applianceconstructed in accordance with the present invention;

FIG. 5 is a plan view of a top portion of a cooking chamber of theappliance;

FIG. 6 is schematic drawing of a control circuit in accordance with thepresent invention;

FIG. 7 a is chart showing a waveform of the control circuit at a firstlevel of operation;

FIG. 7 b is chart showing a waveform of the control circuit at anotherlevel of operation; and

FIG. 7 c is chart showing a waveform of the control circuit at a furtherlevel of operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With initial reference to FIGS. 1-3, a cooking appliance constructed inaccordance with the present invention is generally indicated at 2. Asshown, cooking appliance 2 includes a base frame 3 to which is securedan outer cabinet shell 4 having top and opposing side panels 6-8.Cooking appliance 2 is also provided with a front face or wall 9 and arear panel 10. Arranged at a lower portion of front wall 9 is an intakeair vent 12 through which, as will be discussed more fully below, anambient air flow enters into cabinet shell 4. In addition, cabinet shell4 includes a plurality of air discharge vents, indicated generally at14, arranged on side panel 7. Vents 14 enable cooling air to exit fromwithin cooking appliance 2, thereby removing heat from within cabinetshell 4. Cabinet shell 4 is secured over base frame 3 through aplurality of fasteners 16, with the fasteners 16 arranged along frontwall 9 being secured at tabs 17 (see FIG. 3).

As best seen in FIG. 2, arranged within cabinet shell 4 is a cookingchamber 20 having top, bottom, rear and opposing side walls 21-25. In amanner known in the art, a door 29 is pivotally mounted to front wall 9to selectively enable access to cooking chamber 20. Toward that end,door 29 includes a handle 30 and a window 31 for viewing the contents ofcooking chamber 20 during a cooking operation. Although not shown,window 31 includes a screen (not shown) that prevents microwave energyfields from escaping from within cooking chamber 20 during a cookingoperation. Handle 30 is adapted to interconnect to upper and lowerlatching mechanisms 34 and 35 so as to retain door 29 in a closedposition and prevent operation of cooking appliance 2 whenever door 29is opened.

Cooking appliance 2 is shown to include upper and side control panels 39and 40, each of which includes a respective set of control buttons orelements 41 and 42. The sets of control elements 41 and 42, incombination with a digital display 44, enable a user to establishparticular cooking operations for cooking appliance 2. For instance,control elements 41 can be used to establish the heating parameters ofcooking appliance 2, while control elements 42 enable stored cookingtimes and/or operations to be readily selected. Since the generalprogramming of cooking appliance 2 does not form part of the presentinvention, these features will not be described further herein.

As further shown in FIG. 2, cooking appliance 2 includes a plenum cover62 arranged at an upper portion of cooking chamber 20. As will bediscussed more fully below, plenum cover 62 includes a plurality ofopenings, indicated generally at 63, that enable an exhaust air flow topass from cooking chamber 20. Arranged behind plenum cover 62 is abifurcated air plenum 67 (see FIG. 4) that provides air flow managementfor cooking chamber 20 during a cooking operation. More specifically, anair emitter plate 72 extends rearward from a lower portion of plenumcover 62 to rear wall 23 of cooking chamber 20. In accordance with apreferred embodiment of the invention, air emitter plate 72 includes aplurality of strategically placed openings 73 that are exposed to alower portion of bifurcated plenum 67. A radiant heating device 80,including first and second radiant heating elements 82 and 83 (see FIG.2), preferably extends along air emitter plate 72. More specifically,radiant heating elements 82 and 83 are constituted by sheathed, electricresistive elements, each having a serpentine-like pattern that extendsfore-to-aft across a section of air emitter plate 72. In the mostpreferred embodiment, each heating element 82, 83 is capable ofdelivering 900 watts of energy into cooking chamber 20. More preferably,each heating element 82, 83 is configured to produce 60 watts/in² ofpower. Cooking appliance 2 also includes a convection air intake vent 85having a plurality of convection air openings 86 positioned on rear wall23 of cooking chamber 20.

As shown best with reference to FIGS. 3 and 4, cooking appliance 2includes a microwave heating device 100 incorporating first and secondmagnetrons 102 and 103 (see FIG. 3) that are adapted to generate anddirect a combined microwave energy field into cooking chamber 20. Asseen in FIG. 4, first and second magnetrons 102 and 103 includerespective first and second rotating antenna assemblies 107 and 108.Each rotating antenna assembly 107, 108 includes an antenna portion 110,111, a housing portion 113, 114 and a gear member 116, 117 respectively.In accordance with a preferred form of the invention, antenna assemblies107 and 108 are arranged below bottom wall 22 of cooking chamber 20. Infurther accordance with the invention, antenna portions 110 and 111 arerotated so as to develop a uniform, constructive standing microwaveenergy field within cooking chamber 20. That is, antenna assemblies 107and 108 are rotated by a drive motor 120 having a drive gear 121 whichis drivingly connected to each of gears 116 and 117 of antennaassemblies 107 and 108, preferably through a gear train (not shown).

Referring to FIG. 3, magnetrons 102 and 103 are arranged in a microwavehousing portion 131 of cooking appliance 2. Microwave housing portion131 includes an angled divider 133 and a vertical divider 134. Althoughnot shown, vertical divider 134 is formed with an opening leadingbeneath magnetron 102. In order to prevent magnetrons 102 and 103 fromoverheating, cooking appliance 2 is provided with a microwave coolingsystem 135 that includes a blower assembly 136 which is drivinglyconnected to a drive motor 138 positioned within a duct 139. Duct 139extends from drive motor 138 to an opening 141 arranged below angleddivider 133. With this arrangement, activation of cooking appliance 2causes drive motor 138 to rotate, whereby blower assembly 136establishes a cooling air flow. The cooling air flow is guided throughopening 141 toward magnetron 103 due to the presence of angled divider133. The cooling air flow circulates about magnetron 103, throughvertical divider 134, across magnetron 102 and up along angled divider133, in order to provide a cooling effect for magnetrons 102 and 103,before exiting cooking appliance 2 through vents 14.

In addition to microwave cooling system 135, cooking appliance 2includes an air intake system 160 having an associated drive motor 162coupled to an impeller 163. Drive motor 162 rotates impeller 163 so asto draw in an ambient air flow A through intake air vent 12. Intake airvent 12 leads to an intake air duct 166, while passing about drive motor120 for antenna assemblies 107 and 108. A majority of the air flow A iscirculated within a rear control housing portion 170 in order to cool aplurality of electronic components 172, including a main control board175 which is adapted to receive input and/or programming instructionsthrough control elements 41, 42 in order to establish and set variouscooking operations for cooking appliance 2.

In addition to driving impeller 163, drive motor 162 operates aconvection fan 200 positioned within a convection fan housing 202 that,in the embodiment shown, is arranged behind rear wall 23 of cookingchamber 20. More specifically, convection fan 200 is drivingly connectedfor concurrent rotation with impeller 163 through a drive shaft 205 suchthat operation of drive motor 162 is translated to convection fan 200 toestablish a convective air flow B. Convective air flow B is passed overa convection air heating element 210 and delivered into cooking chamber20 through openings 73 in air emitter plate 72. More specifically, aswill be discussed further below, convective air flow B is directed intobifurcated air plenum 67 before passing into cooking chamber 20.

In further accordance with the preferred form of the invention,bifurcated air plenum 67 includes an angled divider plate 216 thatdefines a tapered air delivery portion 220 and a corresponding taperedexhaust portion 221. In the embodiment shown, air delivery portion 220is essentially defined by air emitter plate 72, angled divider plate 216and part of rear wall 23, while exhaust portion 221 is defined by plenumcover 62, top wall 21 and angled divider plate 216. In any event, airflow B developed through operation of convection fan 200 is heated byheating element 210, directed into air delivery portion 220 ofbifurcated air plenum 67 and then lead into cooking chamber 20 throughopenings 73. The tapering of air delivery portion 220 is provided sothat air initially entering bifurcated air plenum 67 from convection fan200 passes through openings 73 in air emitter plate 72 withsubstantially the same pressure as air reaching an end portion (notseparately labeled) of tapered air delivery portion 220.

As a portion of the cooking operation is constituted by convectionheating, convective air flow B circulates about cooking chamber 20. Thisheated air flow has been found to particularly enhance the even cookingof a food item. As further represented in FIG. 4, a first portion ofconvective air flow B passes into convection air intake vent 85 throughopenings 86. The convective air flow B is heated/reheated by heatingelement 210 before being passed back into cooking chamber 20. At thesame time, a second, preferably smaller portion of convective air flow Bpasses through openings 63 in plenum cover 62 and is directed out ofcooking appliance 2. More specifically, plenum cover 62 leads intotapered exhaust portion 221. The exhaust air flow D entering intotapered exhaust portion 221 is passed upward into an exhaust duct 229before exiting through an exhaust outlet 230 that, in the embodimentshown, is arranged at an upper rear portion of cooking appliance 2. Toreplace the lost air flow, convection fan 200 preferably draws orsiphons a portion of air flow A. For this purpose, one or more openings235 are provided in duct 166 in order to introduce fresh ambient air tothe overall, circulating air flow. In this manner, certain cookingeffluents, including moisture and steam, exit cooking chamber 20 throughexhaust outlet 230, while a fresh supply of air is introduced into theremaining, recirculated air flow due to the presence of opening(s) 235.

In further accordance with the present invention, cooking appliance 2includes a conductive heating device 250 that, in the most preferredform of the invention, defines bottom wall 22 of cooking chamber 20.Conductive heating device 250 is preferably constituted by a ceramicstone plate adapted to support food items within cooking chamber 20.Conductive heating device 250 advantageously provides a thermalconduction path for heating and browning of a food item. Morespecifically, upon activation of cooking appliance 2, radiant heatproduced by heating elements 82 and 83 combines with convective air flowB generated by convection fan 200 to heat conduction heating device 250.Conductive heating device 250 is transparent to microwave energy so thatmicrowave energy fields emitted by magnetrons 102 and 103 pass upwardinto cooking chamber 20 and further contribute to the overall cookingoperation. In further accordance with the invention, conductive heatingdevice 250 is supported upon a plurality of support brackets, such asthose indicated at 255 and 256, to enable or facilitate removal ofconductive heating device 250 for cleaning or other purposes.

With particular reference to FIG. 5, air emitter plate 72 is preferablyformed from anodized cast aluminum and provided with a pair offore-to-aft extending recessed channels 280. Recessed channels 280 areprovided with a plurality of openings 284. Heating elements 82 and 83are nested within recessed channels 280 adjacent openings 284. As shown,each heating element 82, 83 includes a pair of electrodes 286 and 287spaced from side walls 24 and 25 by an insulator 290. With this mountingarrangement, not only do heating elements 82 and 83 provide a source ofradiant heat, but convective air flow B passing through openings 284 isheated by the additional thermal energy generated by heating elements 82and 83 as air flow B passes from air delivery portion 210 of air plenum67 into cooking chamber 20. Therefore, by being routed between, acrossand around respective ones of the various strategically placed openings284, heating elements 82 and 83 evenly distribute thermal and infraredenergy to the food being cooked.

With this overall combined cooking arrangement, a food item, forexample, an open-faced sandwich placed within cooking chamber 20, can beexposed to a four-way combination cooking operation, i.e. radiant,microwave, convection and conductive heating techniques. The combinationof the aforementioned heating techniques serves to cook the food item inan expeditious manner, while maintaining the required food quality. Inaddition, combining the aforementioned heating techniques enablescooking appliance 2 to be readily adapted to cook a wide range of fooditems in an efficient and effective manner, while also establishing anoverall compact unit.

The above description of the preferred construction of cooking appliance2 is provided for the sake of completeness and is covered by co-pendingU.S. patent application entitled “Cooking Appliance includingCombination Heating System” filed on even date herewith and incorporatedherein by reference. The present invention is particularly directed tothe arrangement and control of convection fan 200 and heating device 80.To this end, reference is made to FIG. 6 which schematically depicts acircuit of the control system for both convection fan 200 and heatingdevice 80. As provided in accordance with the preferred embodimentshown, a standard 220 volt AC supply current, such as that typicallyemployed in a household for appliances, is utilized. As an AC, 220 voltpower supply is employed, the power is connected between twoout-of-phase sources 300 and 301. This of course is quite different fromthe 110 volt supply typically found in a household, wherein one line isconnected to neutral, while the other line is connected to a hot or livesource. As both incoming lines are active in this case, a relay 310 isprovided in the circuit, particularly for safety reasons. A controller320, including a control board with a microprocessor (not individuallylabeled), is provided to regulate relay 310. Additionally, there isprovided a triac 330 which allows current to travel therethrough onlyupon a signal from controller 320.

Essentially, triac 330 provides the capability of turning the power lineon or off at various times. Rather than turning triac 330 on and keepingtriac 330 on all the time during operation of cooking appliance 2, inaccordance with the present invention, controller 320 only turns triac330 on at various points in the AC waveform, i.e., a waveform choppingoperation is performed, to effectively lower the overall power load.When a control signal from controller 320 is removed, triac 330automatically turns off at the next zero crossing of the AC waveform. Byturning the AC voltage on at various points in the AC waveform, triac330 is essentially limiting the power going through the device or load,in this case, both convection fan 220 and heating device 80simultaneously. At this point, it should be noted that other devices orloads, such as heating element 210, could be controlled in this manneras set forth in accordance with the present invention.

Turning now to FIGS. 7 a-7 c, there is shown an example of the waveformproduced by the controller 320 in combination with triac 330. Inparticular, this waveform is specifically for convection fan 220. Note,at a high level, when convection fan 220 is 100% on as shown in FIG. 7a, the AC waveform is a standard output AC waveform with no chopping. Inother words, triac 330 is essentially on all the time and allows thepassage of current. As represented in FIG. 7 b, the speed of convectionfan 220 has been reduced. The reduction actually occurs after thewavepoint hits a zero point. More specifically, there is a delay beforetriac 330 turns on and thus passes current as clearly marked in thisfigure. Finally, as illustrated in FIG. 7 c wherein the speed ofconvection fan 220 has been reduced even further, the delay before triac330 turns on and thus allows current to flow is quite long. Indeedalmost half the waveform is prevented from traveling through triac 330such that convection fan 220 is essentially receiving 50% power.Although described with respect to controlling convection fan 220, triac330 preferably controls both heating device 80 and convection fan 220with this arrangement as indicated in FIG. 6. Therefore, the speed ofconvection fan 220 and the output of heating device 80 can besimultaneously controlled in accordance with the invention.

Based on the above, it should be readily apparent that triac 330 isemployed to create a variable fan speed and variable heater intensity inconvection cooking appliance 2. To accomplish the variance of fan speedand radiated heat output level, relay 310 and triac 330 are added to thecontrol board of controller 320 to perform phase angle firing.Essentially, the AC waveform provided to both the fan motor or theheater resistor travels through triac 330 which is regulated bycontroller 320. Triac 330 is turned on at predetermined point in the ACwaveform, with the delay from a zero point waveform crossing functioningto reduce the amount of power sent to the heater resistor and fan motor.When the signal from controller 320 is removed, triac 330 advantageouslyturns off at the next zero crossing of the AC waveform. In this manner,an operationally and economically effective control system is provided,preferably for multiple power loads simultaneously.

Although described with reference to a preferred embodiment of thepresent invention, it should be readily apparent to one of ordinaryskill in the art that various changes and/or modifications can be madeto the invention without departing from the spirit thereof. In general,the invention is only intended to be limited to the scope of thefollowing claims.

1. A convection cooking appliance comprising: a cabinet including top,bottom rear and opposing side walls; a cooking chamber including top,bottom, rear, opposing side walls and a frontal opening; a door movablymounted relative to the cooking chamber for selectively closing thefrontal opening; a heating device provided in the cabinet for performinga portion of a cooking operation; a convection fan arranged in thecabinet to direct a convective air flow into the cooking chamber; and acontrol system for regulating a speed of the convection fan and anintensity of the heating device during a cooking operation by alteringan AC waveform provided to the convection fan and the heating device,said control system including a triac, as well as a controller forturning on the triac at select points in the AC waveform to create adelay from a zero point crossing of the AC waveform, thereby altering anamount of power sent to each of the convection fan and the heatingdevice.
 2. The cooking appliance according to claim 1, wherein thecontroller turns on the triac continuously to operate the convection fanand the heating device at full power.
 3. The cooking appliance accordingto claim 2, wherein the controller prevents approximately half of the ACwaveform from passing through the triac so as to operate the convectionfan and heating device at half power.
 4. The cooking appliance accordingto claim 1, wherein the AC waveform is generated from first and secondout-of-phase sources.
 5. The cooking appliance according to claim 4,wherein the triac is arranged in series between the second source andthe heating device.
 6. The cooking appliance according to claim 4,further comprising: a relay connected in series between the first sourceand the heating device.
 7. The cooking appliance according to claim 6,wherein the triac is arranged in series between the second source andthe heating device and in parallel with the relay.
 8. A convectioncooking appliance comprising: a cabinet including top, bottom rear andopposing side walls; a cooking chamber including top, bottom, rear,opposing side walls and a frontal opening; a door movably mountedrelative to the cooking chamber for selectively closing the frontalopening; a heating device provided in the cabinet for performing aportion of a cooking operation; a convection fan arranged in the cabinetto direct a convective air flow into the cooking chamber; and means forregulating a speed of the convection fan and an intensity of the heatingdevice during a cooking operation by altering an AC waveform provided tothe convection fan and the heating device, said regulating meansincluding a triac which is turned on at select points in the AC waveformto create a delay from a zero point crossing of the AC waveform, therebyaltering an amount of power sent to each of the convection fan and theheating device.
 9. The cooking appliance according to claim 8, whereinthe regulating means turns on the triac continuously to operate theconvection fan and the heating device at full power.
 10. The cookingappliance according to claim 9, wherein the regulating means preventsapproximately half of the AC wave form to pass through the triac so asto operate the convection fan and heating device at half power.
 11. Thecooking appliance according to claim 8, wherein the AC waveform isprovided by first and second out-of-phase sources.
 12. The cookingappliance according to claim 11, wherein the triac is arranged in seriesbetween the second source of the AC waveform and the heating device. 13.The cooking appliance according to claim 11, wherein the regulatingmeans further comprises a relay connected in series between the firstsource of the AC waveform and the heating device.
 14. The cookingappliance according to claim 11, wherein the triac is arranged in seriesbetween the second source of the AC waveform and the heating device andin parallel with the relay.
 15. A method of performing a cookingoperation while varying a speed of a convection fan and an intensity ofa heating device in a convection cooking appliance: placing a food itemonto a cooking chamber of the cooking appliance; activating a heatingdevice to create heat introduced into the cooking chamber by providingan AC source of power having an AC waveform to the heating device;operating a convection fan to deliver a convective air flow into thecooking chamber by providing the AC source of power having the ACwaveform to the convection fan; and regulating a speed of the convectionfan and an intensity of the heating device during the cooking operationby altering the AC waveform provided to both the convection fan and theheating device by turning on a triac, arranged between the AC source ofpower and each of the convection fan and the heating device, at selectpoints in the AC waveform to create a delay from a zero point crossingof the AC waveform, thereby altering an amount of power sent to each ofthe convection fan and the heating device.
 16. The method of claim 15,wherein the speed of the convection fan and the intensity of the heatingdevice are set at full power by continuously turning on the triac. 17.The method of claim 16, wherein the speed of the convection fan and theintensity of the heating device are set at half power by permitting onlyapproximately half of the AC waveform to pass through the triac.
 18. Themethod of claim 15, further comprising: activating a relay to complete acurrent path to both the convection fan and the heating device.
 19. Themethod of claim 18, further comprising: bypassing the triac uponactivating the relay to complete the current path to both the convectionfan and the heating device.